The present invention relates to apparatuses and methods for manufacturing pressboard, particularly from shredded paper coated with a thermoplastic material.
Papers coated with a thermoplastic material (poly-coated papers) are utilized in a variety of applications. In one such application, kraft paper is coated with polyethylene to create roll headers utilized in the paper manufacturing industry. The use of such headers is discussed in copending application Ser. No. 642,569, filed Aug. 20, 1984, by Lamb, and entitled ROLL HEADER PLATEN, the disclosure of which is incorporated by reference. The thermoplastics used in coating the papers are readily obtained, for example through the recycle of plastic milk bottles and the like, and provide an inexpensive heat-activated adhesive medium.
The use of poly-coated papers inevitably creates waste or scrap paper generated from cutting the desired size blanks from the sheet stock. For example, the poly-coated roll headers are round and therefore leave a relatively large offal portion when cut from rectangular sheet stock. Disposal of the scrap paper is difficult, time consuming, and/or expensive. One option is to dispose of the scrap paper in a land fill. This is expensive both in terms of transporting the paper to the land fill and also in land fill fees. A second option involves incinerating the scrap paper. However, certain regulatory agencies are prohibiting such incineration in many states. Third, the waste scrap paper can be fabricated into a pressboard.
One such apparatus and method for producing pressboard from scrap poly-coated paper is disclosed in U.S. Pat. No. 3,718,536, issued Feb. 27, 1973, to Downs et al, and entitled COMPOSITE BOARD AND METHOD OF MANUFACTURE. The Downs method includes, first, shredding the paper into ribbons of up to two inches in width by eight inches in length; second, air-forming the shredded paper into a bat; third, heating the bat above the softening point of the thermoplastic material; fourth, pressing the heated bat to cause the thermoplastic material to flow and consolidate the bat; and, fifth, cooling the consolidated bat to cure the bat. However, the Downs apparatus and process are capable only of batch processing the scrap paper, restricting throughput and requiring excessive labor in its operation. Although the Downs patent represents that the composite board can be manufactured continuously (column 5, lines 31-42), no operative apparatus or method is disclosed for a continuous implementation.